As the rapid development of the integrated circuit, a more exact requirement directed to a quality of the substrate material is required. For a normal low voltage IGBT, especially for FS-IGBT manufactured by an epitaxy technology at about 600 volts, the technology difficult is the consistency of the thickness and the specific resistance. The major reason of a low consistency of the specific resistance is an auto-dope of the boron impurity and arsenic impurity. Auto-dope of the N-type impurities (arsenic or phosphorus) can be eliminated by adopting a low voltage epitaxy technology. However, the silicon wafer grown by the low voltage epitaxy technology has a great temperature gradient which results to a great deal of stacking fault and dislocation, a great stacking fault density and a dislocation density will bring a fatal damage to the electrical parameter and the yield of the device. At the same time, some research data indicate that in a P/P+ epitaxy technology applied to the doped boron, the auto-dope effect is greater in a low voltage condition than that in a normal voltage. Thus, for the normal P-type substrate, because the injection is done before the epitaxy technology and the substrate material has relative more surface defects, results in relative more defects on the epitaxial layer, and the epitaxy quality is poor, causing the product to have performance problems.
In the conventional low voltage IGBT epitaxy field stop technology, the FS region of the IGBT is firstly formed, then the epitaxial layer with a required thickness and a specific resistance is grown on the material. In such manufacturing technology, because the injection is done before the epitaxy technology and the substrate material has relative more surface defects, results in relative more defects on the epitaxial layer, and the epitaxy quality is poor, causing the product to have obvious defects such as performance problems. First, when the reactant gas in the epitaxy technology traverses the substrate surface, it's concentration reduces constantly, because when it traverses the substrate surface, at the same time, it reacts with silicon substrate. Secondly, the growth rate of the silicon epitaxy changes according to a change of the silicon source concentration. When the silicon source concentration is high, the epitaxy growing rate is high. Otherwise, when the silicon source concentration is low, the epitaxy growing rate is low. In addition, the concentration of the dopant changes according to a change of the concentration of the impurities in the epitaxial layer. When the concentration of the dopant increases, the concentration of the impurities in the epitaxial layer increases, the specific resistance of the epitaxy decreases, the break down voltage decreases. Otherwise, when the concentration of the dopant decreases, the concentration of the impurities in the epitaxial layer decreases, the specific resistance of the epitaxy increases, the break down voltage increases (in fact, the reaction rate does not simply depend upon the concentration of the reactant, but in generally situation, we admit such proportional relation). As described above, the silicon source concentration in the reactant gas decreases constantly, and then the growth rate which is proportional to the silicon source concentration also decreases constantly, and then the evenness and the consistency of the thickness and the specific resistance of the epitaxial layer deteriorate. When an epitaxy growth is performed on a relative small size substrate, such epitaxy parameter deterioration caused by the reaction rate can be accepted. However, when the diameter of the substrate becomes greater, because the substrate material has relative more surface defects, causing such difference to be greater which goes beyond the tolerance range in production.